奥麦罗制药美股招股说明书(2025-11-14版)

Common Stock We have entered into a Controlled Equity OfferingSMSales Agreement (the “sales agreement”) with Cantor Fitzgerald & Co.(“Cantor”) relating to the offer and sale of shares of our common stock. In accordance with the terms of the sales agreement, we mayoffer and sellby means of this prospectus supplement and the accompanying prospectusshares of our common stock, from time totime, having an aggregate offering price of up to $150,000,000 through Cantor acting as sales agent. Our common stock is traded on The Nasdaq Global Market under the symbol “OMER.” On November 13, 2025, the lastreported sale price of our common stock was $6.28 per share. Sales of our common stock under this prospectus supplement and the accompanying prospectus, if any, may be made by anymethod that is deemed to be an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended (the“Securities Act”). This includes sales made directly on The Nasdaq Global Market or sales made to or through a market maker otherthan on an exchange. With our prior written consent, sales may also be made in negotiated transactions at market prices prevailing atthe time of sale or at prices related to such prevailing market prices or any other method permitted by law. Cantor is not required tosell any specific number or dollar amount of securities, but will act as a sales agent using commercially reasonable efforts consistentwith its normal trading and sales practices, to sell on our behalf shares of our common stock as designated by us. There is noarrangement for funds to be received in any escrow, trust or similar arrangement. Cantor will be entitled to compensation under the terms of the sales agreement at a fixed commission rate of up to 3.0% ofthe gross sales price per share sold under the sales agreement. See “Plan of Distribution” beginning on page S-10for additionalinformation regarding Cantor’s compensation. In connection with the sale of common stock on our behalf, Cantor will be deemed tobe an “underwriter” within the meaning of the Securities Act and the compensation of Cantor will be deemed to be underwritingcommissions or discounts. We have also agreed to provide indemnification to Cantor against certain liabilities, including liabilitiesunder the Securities Act. Investing in our common stock involves significant risks. Before buying shares of our common stock, you shouldcarefully consider the risks described under the caption “Risk Factors” beginning on page S-4 of this prospectus supplementand in the documents incorporated by reference into this prospectus supplement. Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved ordisapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanyingprospectus. Any representation to the contrary is a criminal offense. Cantor The date of this prospectus supplement is November 14, 2025 TABLE OF CONTENTS Prospectus Supplement About this Prospectus SupplementForward-Looking StatementsProspectus Supplement SummaryThe OfferingRisk FactorsUse of ProceedsDilutionPlan of DistributionLegal MattersExpertsWhere You Can Find More InformationIncorporation By Reference Prospectus About This ProspectusForward-Looking StatementsAbout OmerosWhere You Can Find More InformationIncorporation by ReferenceRisk FactorsUse of ProceedsDescription of Common StockDescription of Preferred StockDescription of Debt SecuritiesDescription of Depositary SharesDescription of WarrantsDescription of Subscription RightsDescription of UnitsPlan of DistributionLegal MattersExperts ABOUT THIS PROSPECTUS SUPPLEMENT This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offeringof common stock and updates the information contained in the accompanying prospectus and the documents incorporated by referenceherein and therein. The second part is the accompanying prospectus, which provides more general information, some of which doesnot apply to this offering. If information included or incorporated by reference in this prospectus supplement is inconsistent with theaccompanying prospectus or the information incorporated by reference therein, then this prospectus supplement or the informationincorporated by reference in this prospectus supplement will apply and will supersede the information in the accompanying prospectusand the documents incorporated by reference therein. For a more detailed understanding of our common stock, you should read boththis prospectus supplement and the accompanying prospectus, together with additional information described under the heading“Where You Can Find More Information.” This prospectus supplement is part of a shelf registration statement on Form S-3 (File No.333-291522) that went effectiveupon filing with the SEC on November 14, 2025. Under the shelf registration process, we may from